Karma model. Temporal alternation

We add excitation cI(t) with period T to the system
    dE/dt = F(E, n) + c I(t) = [A - (n/nb)M][1 - tanh(E - 3)]E2/2 - E + c I(t),
    dn/dt = H(E, n) = ε [Θ(E - 1) - n].
where A = 1.5415 and I(t) ~ [cos(πt/T)]500,   -δ ∫ δI(t)dt = 1.

M nb ε c T

dt Ymax field
To the right E(t)/4 excitation (black) and n(t) recovery (blue) variables are plotted. For small T the system is not relaxed before the second excitation cycle.

Heart rhythms     updated 2 Dec 2011